Lymphoma is the most common tumour in hamsters. Hamster papilloma virus (HaPV) is seem to be the cause of this tumour this virus is belonging to the subgroup Papovaviridae and also causes keratinizing skin tumours of hair follicle origin.

Lymphomas are usually arise in the mesentery, but can originate in the axillary and cervical lymph nodes the tumours are frequently lymphoid but in older hamsters lymphoma are most commonly observed neoplasms of haematopoietic system.

In our study a 2.5 years old male Syrian hamster was referred to small animal hospital of Tehran university veterinary faculty. The systemic condition and respiration was not in good states and there was a history of anorexia for about one week in palpation of the abdomen there was a great mass palpable. Radiography confirmed the presence of that mass.

The hamster euthanized by thiopental Na by the request of the owner. in necropsy there was a huge mass that filled approximately all of the abdomen. It seemed to be originated from mesentery. the mass involved the gastrointestinal wall and lymph nodes. Kidneys, liver, gonads and spleen were seemed normal. At dissection of the mass the centre was necrosis and surrounded with a layer of approximately 2.5 cm. samples were obtained from the mass and other organs. These tissues were fixed in 10% neutral buffered formalin, embedded in paraffin, sectioned and stained with hematoxylin and eosin.

In light microscope examination solid sheets of lymphoid cells interspersed with variable numbers of other lymphoid types like immunoblast. They had a high mitotic index .reticular cells and macrophages scattered between lymphoid cells. This is the first report of hamster lymphoma in Iran.